Finely divided highly transparent diketopyrrolopyrrole pigments

Abstract

Finely divided 1,4-diketopyrrolo[3,4-c]pyrroles of the formula ##STR1## where A and B are each independently of the other a radical of the formula ##STR2## wherein at least 84% by weight of the particles have a Stokes equivalent diameter of ≦0.25 μm, and mixtures thereof. The substituents R 1 and R 2 are defined in claim 1. These pigments are notable for a very pure hue and outstanding transparency.

What is claimed is: 
     
       1. Finely divided 1,4-diketopyrrolo[3,4-c]pyrroles of the formula ##STR10## where A and B are each independently of the other a radical of the formula ##STR11## where R 1  and R 2  are each independently of the other hydrogen, halogen, C 1  -C 5  alkyl or phenyl, wherein at least 84% by weight of the particles have a Stokes equivalent diameter of ≦0.25 μm, and mixtures thereof. 
     
     
       2. 1,4-Diketopyrrolo[3,4-c]pyrroles of the formula I according to claim 1, wherein at least 84% by weight of the particles have a Stokes equivalent diameter of ≦0.20 μm. 
     
     
       3. 1,4-Diketopyrrolo[3,4-c]pyrroles according to claim 2, wherein, in the formula I, A and B are independently of each other radicals of the formulae ##STR12## 
     
     
       4. 1,4-Diketopyrrolo[3,4-c]pyrroles according to claim 2, wherein, in the formula I, A and B are identical and are radicals of the formulae ##STR13## 
     
     
       5. 1,4-Diketopyrrolo[3,4-c]pyrroles according to claim 2, comprising a solid solution of the compounds of the formulae ##STR14## 
     
     
       6. A 1,4-diketopyrrolo[3,4-c]pyrrole of the formula ##STR15## according to claim 2, having a CIELAB chroma C* ab  ≧42 in 1% concentration in a 1.0 mm thick compression-moulded masstone PVC-P sheet produced according to DIN 53775 Parts 2 and 7. 
     
     
       7. A 1,4-diketopyrrolo[3,4-c]pyrrole of the formula ##STR16## according to claim 2, having a CIELAB chroma C* ab  ≧42 in 1% concentration in a 1.0 mm thick compression-moulded masstone PVC-P sheet produced according to DIN 53775 Parts 2 and 7. 
     
     
       8. A 1,4-diketopyrrolo[3,4-c]pyrrole of the formula ##STR17## according to claim 2, having a CIELAB chroma C* ab  ≧14 in 1% concentration in a 1.0 mm thick compression-moulded masstone PVC-P sheet produced according to DIN 53775 Parts 2 and 7. 
     
     
       9. The solid solution of the 1,4-diketopyrrolo[3,4-c]pyrroles according to claim 5, having a CIELAB chroma C* ab  >36 in 1% concentration in a 1.0 mm thick compression-moulded masstone PVC-P sheet produced according to DIN 53775 Parts 2 and 7. 
     
     
       10. A process for preparing 1,4-diketopyrrolo[3,4-c]pyrroles of the formula I according to claim 1 by reacting in a 1:2 molar ratio 1 mol of dicyclohexyl, dialkyl, alkyl phenyl or diphenyl succinate in which alkyl is C 1  -C 18  alkyl and phenyl is unsubstituted phenyl or phenyl substituted by one or two halogen atoms or one or two C 1  -C 6  alkyl or C 1  -C 6  alkoxy groups with 2 mol of a mixture of nitriles of the formulae   A-CN                                                       (III)     and     B-CN                                                       (IV),     where A and B are each as defined above and ACN and BCN in the nitrile mixture are in a molar ratio of 100:0 to 50:50 relative to each other, in an inert organic solvent in the presence of an alkali metal or an alkali metal alkoxide as strong base at a temperature of from about 60° C. to about 140° C. to form a pigment alkali metal salt and then liberating a compound of formula I by protonating the resulting pigment alkali metal salt and subsequent conditioning, which comprises discharging the pigment alkali metal salt suspension into water and/or an alcohol ROH, where R is C 1  -C 4  alkyl, at a temperature between -20° C. and 50° C. in the presence of an acid and treating it likewise at a temperature between -20° C. and 50° C. for 10 minutes to 48 hours.   
     
     
       11. A process according to claim 10, wherein the acid is added to the water and/or alcohol before or together with the alkali metal pigment salt suspension. 
     
     
       12. A process according to claim 10, wherein the radicals A and B are each independently of the other ##STR18## 
     
     
       13. A process according to claim 10, wherein the radicals A and B are identical. 
     
     
       14. A process according to claim 10, wherein a mixture of water and alcohol in a ratio of 80-20:20-80% by volume is used. 
     
     
       15. A process according to claim 10, wherein the alcohol is methanol or ethanol. 
     
     
       16. A process according to claim 10, wherein the acid is used in a sufficient amount to obtain pH<10 at the end of the protonation. 
     
     
       17. A process according to claim 10, wherein the protonation is effected using an inorganic acid selected from hydrochloric acid, sulfuric acid and phosphoric acid. 
     
     
       18. A process according to claim 10, wherein the protonation is effected using an aliphatic or aromatic carboxylic or sulfonic acid selected from formic acid, acetic acid, propionic acid, butyric acid, hexanoic acid, oxalic acid, benzoic acid, phenylacetic acid, benzenesulfonic acid and p-toluenesulfonic acid. 
     
     
       19. A process according to claim 17, wherein sulfuric acid is used. 
     
     
       20. A process according to claim 18, wherein acetic acid or formic acid are used. 
     
     
       21. A process according to claim 10, wherein the protonating agent is used in any desired mixing ratios between 5 and 20 parts by weight of the protonating agent per 1 part of the alkali metal pigment salt. 
     
     
       22. A process according to claim 10, wherein protonation and conditioning are carried out at a temperature between -10° and 30° C.